Inherently crosslinkable polyamides

ABSTRACT

A polyamide which contains a monoolefinically unsaturated compound chemically bonded at the end of the polymer chain, a process for preparing this polyamide, a polyamide obtainable by crosslinking this polyamide, and also fibers, films, and moldings, comprising at least one such polyamide.

TECHNICAL FIELD

The present invention relates to a polyamide which contains amonoolefinically unsaturated compound chemically bonded to the end ofthe polymer chain.

It further relates to a process for preparing this polyamide, to apolyamide obtainable by crosslinking this polyamide, and to fibers,films, and moldings comprising at least one such polyamide.

BACKGROUND ART

Polyamides, in particular nylon-6, and nylon-6,6, are industriallysignificant polymers. They are usually prepared by reacting suitablemonomers such as caprolactam, adipic acid, or hexamethylenediamine, inthe presence of water.

Unless further measures are taken, this gives polyamides which duringdownstream steps of processing, such as injection molding, have atendency to undergo uncontrolled molecular weight increase with aresultant impairment of processing properties. In particular, anincrease in melt viscosity occurs (determined as a fall-off in the meltvolume flow rate to EN ISO 1133), and in injection molding, for example,this leads to longer cycle time.

To stabilize the polyamide with respect to this type of uncontrolledmolecular weight increase, it is usual to use chain regulators duringthe preparation of the polymer, an example being propionic acid.

These chain regulators can substantially suppress the molecular weightincrease but in order to shorten cycle times in injection molding it isdesirable to increase the melt volume flow rate of polyamides to EN ISO1133 while the relative viscosity determined to DIN 51562-1 to -4,remains the same.

It is an object of the present invention to provide a process which, ina technically simple and cost-effective manner, permits the preparationof a polyamide which when compared with polyamides chain-regulated byconventional methods has higher melt volume flow rate to EN ISO 1133while the relative viscosity determined to DIN 51562-1 to -4, remainsthe same.

DISCLOSURE OF THE INVENTION

We have found that this object is achieved by means of the polyamidedefined at the outset, a process for its preparation, a polyamideobtainable by crosslinking this polyamide, and fibers, films, andmoldings, comprising at least one such polyamide.

For the purposes of the present invention, polyamides are homopolymers,copolymers, mixtures, and grafts of synthetic long-chain polyamideswhich have repeat amide groups as a substantial constituent in the mainpolymer chain. Examples of these polyamides are nylon-6(polycaprolactam), nylon-6,6 (polyhexamethyleneadipamide), nylon-4,6(polytetramethylene-adipamide), nylon-6,10(polyhexamethylenesebacimide), nylon-7 (polyenantholactam), nylon-11(polyundecanolactam), nylon-12 (polydodecanolactam). These polyamidesare known by the generic name nylon. For the purposes of the presentinvention, polyamides also include those known as aramids (aromaticpolyamides), such as polymetaphenyleneisophthalimide (NOMEX® Fiber, U.S.Pat. No. 3,287,324), and polyparaphenyleneterephthalamide (KEVLAR®Fiber, U.S. Pat. No. 3,671,542).

MODE(S) FOR CARRYING OUT THE INVENTION

The preparation of polyamides may in principle take place by twomethods.

During the polymerization of dicarboxylic acids and diamines, orpolymerization of amino acids or derivatives of these, such asaminocarboxylic nitrites, aminocarboxamides, aminocarboxylic esters, oraminocarboxylic salts, the amino end groups and carboxy end groups ofthe starting monomers or starting oligomers react with one another toform an amide group and water. The water can then be removed from thepolymer. During the polymerization of aminocarboxamides, the amino andamide end groups of the starting monomers or starting oligomers reactwith one another to form an amide group and ammonia. The ammonia canthen be removed from the polymer. During the polymerization ofaminocarboxylic esters, the amino and ester end groups of the startingmonomers or starting oligomers react with one another to form an amidegroup and an alcohol. The alcohol can then be removed from the polymer.During the polymerization of aminocarboxylic nitrites the nitrile groupsmay firstly be reacted with water to give amide groups or carboxylicacid groups, and the resultant aminocarboxamides or aminocarboxylicacids can be reacted as described. This polymerization reaction isusually termed polycondensation.

The polymerization of lactams as starting monomers or starting oligomersis usually termed polyaddition.

The polyamides can be obtained by processes known per se, for examplethose described in DE-A-14 95 198, DE-A-25 58 480, EP-A-129 196 or in:Polymerization Processes, Interscience, New York, 1977, pp. 424-467, inparticular pp. 444-446, from monomers selected from the group consistingof lactams, omega-amino-carboxylic acids, omega-aminocarbonitriles,omega-aminocarboxamides, omega-aminocarboxylic salts,omega-aminocarboxylic esters, equimolar mixtures of diamines anddicarboxylic acids, dicarboxylic acid/diamine salts, dinitriles anddiamines, or mixtures of these monomers.

Monomers which may be used are

a C₂-C₂₀, preferably C₂-C₁₈, arylaliphatic or preferably aliphaticlactam in the form of monomer or oligomer, examples being enantholactam,undecanolactam, dodecanolactam or caprolactam,

C₂-C₂₀, preferably C₃-C₁₈, aminocarboxylic acids in the form of monomeror oligomer, examples being 6-aminocaproic acid, 11-aminoundecanoicacid, and the salts of these, such as alkali metal salts, e.g. lithiumsalts, sodium salts, potassium salts,

C₂-C₂₀, preferably C₃-C₁₈, aminocarbonitriles in the form of monomer oroligomer, examples being 6-aminocapronitrile, 11-aminoundecanonitrile,

C₂-C₂₀ aminocarboxamines in the form of monomer or oligomer, examplesbeing 6-aminocapramide, 11-aminoundecanoamide,

esters, preferably C₁-C₄-alkyl esters, e.g. methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl esters, of C₂-C₂₀, preferablyC₃-C₁₈, aminocarboxylic acids, examples being 6-aminocaproates, such asmethyl 6-aminocaproate, 11-aminoundecanoates, such as methyl11-aminoundecanoate,

a C₂-C₂₀, preferably C₂-C₁₂, alkyldiamine, such as tetramethylenediamineor preferably hexamethylenediamine,

with a C₂-C₂₀, preferably C₂-C₁₄, aliphatic dicarboxylic acid or itsmono- or dinitrile, examples being sebacic acid, dodecanedioic acid,adipic acid, sebaconitrile, decanonitrile, or adiponitrile,

a C₂-C₂₀, preferably C₂-C₁₂, alkyldiamine in the form of monomer oroligomer, examples being tetramethylenediamine or preferablyhexamethylenediamine,

with a C₈-C₂₀, preferably C₈-C₁₂, aromatic dicarboxylic acid orderivatives thereof, such as chlorides, examples being2,6-naphthalenedicarboxylic acid, and preferably isophthalic acid orterephthalic acid,

a C₂-C₂₀, preferably C₂-C₁₂, alkyldiamine in the form of monomer oroligomer, examples being tetramethylenediamine or preferablyhexamethylenediamine,

with a C₉-C₂₀, preferably C₉-C₁₈, arylaliphatic dicarboxylic acid orderivatives thereof, such as chlorides, examples being o-, m- orp-phenylenediacetic acid,

a C₆-C₂₀, preferably C₆-C₁₀, aromatic diamine in the form of monomer oroligomer, examples being m- and p-phenylenediamine,

with a C₂-C₂₀, preferably C₂-C₁₄, aliphatic dicarboxylic acid or mono-or dinitriles thereof, examples being sebacic acid, dodecanedioic acid,adipic acid, sebaconitrile, decanonitrile, or adiponitrile,

a C₆-C₂₀, preferably C₆-C₁₀, aromatic diamine in the form of monomer oroligomer, examples being m- and p-phenylenediamine,

with a C₈-C₂₀, preferably C₈-C₁₂, aromatic dicarboxylic acid orderivatives thereof, such as chlorides, examples being2,6-naphthalenedicarboxylic acid, and preferably isophthalic acid orterephthalic acid,

a C₆-C₂₀, preferably C₆-C₁₀, aromatic diamine in the form of monomer oroligomer, examples being m- and p-phenylenediamine,

with a C₉-C₂₀, preferably C₉-C₁₈, arylaliphatic dicarboxylic acid orderivatives thereof, such as chlorides, examples being o-, m-, andp-phenylenediacetic acid,

a C₇-C₂₀, preferably C₈-C₁₈, arylaliphatic diamine in the form ofmonomer or oligomer, examples being m- and p-xylylenediamine,

with a C₂-C₂₀, preferably C₂-C₁₄, aliphatic dicarboxylic acid or mono-or dinitriles thereof, examples being sebacic acid, dodecanedioic acid,adipic acid, sebaconitrile, decanonitrile, and adiponitrile,

a C₇-C₂₀, preferably C₈-C₁₈, arylaliphatic diamine in the form ofmonomer or oligomer, examples being m- and p-xylylenediamine,

with a C₆-C₂₀, preferably C₆-C₁₀, aromatic dicarboxylic acid orderivatives thereof, such as chlorides, examples being2,6-naphthalenedicarboxylic acid, or preferably isophthalic acid orterephthalic acid,

a C₇-C₂₀, preferably C₈-C₁₈, arylaliphatic diamine in the form ofmonomer or oligomer, examples being m- and p-xylylenediamine,

with a C₉-C₂₀, preferably C₉-C₁₈, arylaliphatic dicarboxylic acid orderivatives thereof, such as chlorides, examples being o-, m-, andp-phenylenediacetic acid,

and also homopolymers, copolymers, mixtures, and grafts of thesestarting monomers or starting oligomers.

Particular oligomers which may be used are the dimers, trimers,tetramers, pentamers, or hexamers of the monomers mentioned, or ofmixtures of these monomers.

In one preferred embodiment, the lactam used is caprolactam, the diamineused comprises tetramethylenediamine, hexamethylenediamine, or a mixtureof these, and the dicarboxylic acid used comprises adipic acid, sebacicacid, dodecanedioic acid, terephthalic acid, isophthalic acid, or amixture of these. Caprolactam is particularly preferred as lactam, asare hexamethylenediamine as diamine and adipic acid or terephthalic acidor a mixture of these as dicarboxylic acid.

Particular preference is given here to those starting monomers orstarting oligomers which during the polymerization give the polyamidesnylon-6, nylon-6,6, nylon-4,6, nylon-6,10, nylon-6,12, nylon-7,nylon-11, nylon-12 or the aramids polymetaphenylene-isophthalamide orpolyparaphenyleneterephthamide, in particular to those which givenylon-6 or nylon-6,6.

In one preferred embodiment, use may be made of one or more chainregulators during preparation of the polyamides. Compounds which may beused advantageously as chain regulators are those which have one ormore, for example two, three, or four, and in the case of systems in theform of fibers preferably two, amino groups reactive in polyamideformation, or one or more, for example two, three, or four, and in thecase of systems in the form of fibers preferably two, carboxy groupsreactive in polyamide formation.

In the first case the result is polyamides in which the monomers andchain regulators used to prepare the polyamide have more of the aminegroups used to form the polymer chain, or of their equivalents, than ofcarboxylic acid groups used to form the polymer chain, or theirequivalents.

In the second case the result is polyamides in which the monomers andchain regulators used to prepare the polyamide have more of thecarboxylic acid groups used to form the polymer chain, or of theirequivalents, than of amine groups used to form the polymer chain, ortheir equivalents.

Chain regulators which may be used with advantage are monocarboxylicacids, examples being alkanecarboxylic acids, such as acetic acid andpropionic acid, and other examples being a benzene- ornaphthalenemonocarboxylic acid, such as benzoic acid, and dicarboxylicacids, such as C₄-C₁₀ alkanedicarboxylic acid, e.g. adipic acid, azelaicacid, sebacic acid, dodecanedioic acid, C₅-C₈ cycloalkanedicarboxylicacid, for example cyclohexane-1,4-dicarboxylic acid, or a benzene- ornaphthalenedicarboxylic acid, such as terephthalic acid, isophthalicacid, naphthalene-2,6-dicarboxylic acid, and C₂-C₂₀, preferably C₂-C₁₂,alkylamines, such as cyclohexylamine, C₆-C₂₀, preferably C₆-C₁₀,aromatic monoamines, such as aniline, or C₇-C₂₀, preferably C₈-C_(18,)arylaliphatic monoamines, such as benzylamine, and C₄-C₁₀alkanediamines, e.g. hexamethylenediamine.

The chain regulators may be unsubstituted or substituted, for examplewith aliphatic groups, preferably C₁-C₈-alkyl groups, such as methyl,ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, n-pentyl,n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, OH, ═O, C₁-C₈-alkoxy, COOH,C₂-C₆-carbalkoxy, C₁-C₁₀-acyloxy, or C₁-C₈-alkylamino, or sulfonic acidor salts thereof, such as alkali metal or alkaline earth metal salts,cyano, or halogens, such as fluorine, chlorine, bromine. Examples ofsubstituted chain regulators are sulfoisophthalic acid, the alkali metalor alkaline earth metal salts thereof, such as the lithium salts, sodiumsalts, or potassium salts, sulfoisophthalic esters, for example thosewith C₁-C₁₆ alkanols, and sulfoisophthalic mono- or diamides, inparticular with monomers suitable for forming polyamides and bearing atleast one amino group, for example hexamethylenediamine or6-aminocaproic acid.

Chain regulators used with preference are sterically hindered piperidinederivatives of the formula

where

-   -   R¹ is a functional group capable of amide formation with respect        to the polymer chain of the polyamide, preferably a —(NH)R⁵        group, where R⁵ is hydrogen or C₁-C₈-alkyl, or is a carboxy        group or a carboxy derivative or a —(CH₂)_(x)(NH)R⁵ group where        X is from 1 to 6 and R⁵ is hydrogen or C₁-C₈-alkyl, or is a        —(CH₂)_(y)COOH group where Y is from 1 to 6, or is an acid        derivative of —(CH₂)_(y)COOH where Y is from 1 to 6, and in        particular is an —NH₂ group,    -   R² is an alkyl group, preferably a C₁-C₄-alkyl group, such as        methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,        sec-butyl, sec-butyl, in particular a methyl group,    -   R³ is hydrogen, C₁-C₄-alkyl, or O—R⁴, where R⁴ is hydrogen or        C_(l)-C₇-alkyl, and in particular R³ is hydrogen.

In compounds of this type, steric hindrance usually prevents reaction ofthe tertiary, and in particular the secondary, amino groups of thepiperidine ring system.

A particularly preferred sterically hindered piperidine derivative is4-amino-2,2,6,6-tetramethylpiperidine.

A chain regulator may be used advantageously in amounts of at least0.001 mol %, preferably at least 0.01 mol %, in particular at least 0.03mol %, particularly preferably at least 0.08 mol %, based on 1 mole ofamide groups of the polyamide.

A chain regulator may advantageously be used in amounts of not more than2.0 mol %, preferably not more than 1 mol %, in particular not more than0.6 mol %, particularly preferably not more than 0.5 mol %, based on 1mole of amide groups of the polyamide.

According to the invention, the polyamide contains a monoolefinicallyunsaturated compound chemically bonded at the end of the polymer chain.

For the purposes of the present invention, the term monoolefinicallyunsaturated compound includes mixtures of these monoolefinicallyunsaturated compounds.

As monoolefinically unsaturated compound it is advantageous to use amonoolefinically unsaturated monocarboxylic acid.

As monoolefinically unsaturated compound it is advantageous to use amonoolefinically unsaturated monoamine.

As monoolefinically unsaturated compound use may advantageously be madeof a terminally olefinically unsaturated compound.

In the case of a monoolefinically unsaturated monocarboxylic acid asmonoolefinically unsaturated compound, use may in particular be made ofa terminally olefinically unsaturated, linear, unbranchedalkenemonocarboxylic acid, particularly preferably one of the formulaCH₂═CH—(CH₂)_(n)—COOHwhere n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, in particular 3.

The monoolefinically unsaturated monocarboxylic acids and theirpreparation are known per se.

The monoolefinically unsaturated monoamines and their preparation areknown per se.

The content of monoolefinically unsaturated compound may advantageouslybe at least 0.001 mol %, preferably at least 0.01 mol %, in particularat least 0.03 mol %, particularly preferably at least 0.08 mol %, basedon 1 mole of amide groups of the polyamide.

The content of monoolefinically unsaturated compound may advantageouslybe not more than 2.0 mol %, preferably not more than 1 mol %, inparticular not more than 0.6 mol %, particularly preferably not morethan 0.5 mol %, based on 1 mole of amide groups of the polyamide.

The polyamides of the invention can be obtained by reacting suitablemonomers, oligomers, or mixtures of these suitable for forming apolyamide to give a polyamide in the presence of a monoolefinicallyunsaturated compound or a compound which under the reaction conditionsfor preparing the polyamide makes available the monoolefinicallyunsaturated compound.

The compound used to make available the monoolefinically unsaturatedmonocarboxylic acid under the reaction conditions for preparing thepolyamide may be one where the olefinic double bond is made availableunder the reaction conditions, for example an amino acid which forms thecorresponding monoolefinically unsaturated monocarboxylic acid withelimination of ammonia, or a hydroxy acid which forms the correspondingmonoolefinically unsaturated monocarboxylic acid with elimination ofwater. In the case of the preferred terminal olefinically unsaturatedmonocarboxylic acids, particular preference is given to the terminalamino or hydroxy compounds. The compounds may also be those where thecarboxylic acid group is made available under the reaction conditions,for example nitrites, esters, or amides. The compounds used to makeavailable the monoolefinically unsaturated monocarboxylic acid under thereaction conditions for preparing the polyamide may also be a compoundwhere both the olefinic double bond and the carboxylic acid group aremade available under the reaction conditions, for example aminonitrites, amino esters, amino amides, hydroxy nitrites, hydroxy esters,or hydroxy amides.

The compound used to make available the monoolefinically unsaturatedmonoamine under the reaction conditions for preparing the polyamide maybe a compound where the olefinic double bond is made available under thereaction conditions, for example a diamine which forms the correspondingmonoolefinically unsaturated monoamine with elimination of ammonia, or ahydroxy amine which forms the corresponding monoolefinically unsaturatedmonoamine with elimination of water. In the case of the preferredterminal olefinically unsaturated monoamines, particular preference isgiven to the terminal amino or hydroxy compounds. Use may also be madeof compounds where the amine group is made available under the reactionconditions, for example amides. Other compounds which can be used tomake available the monoolefinically unsaturated monoamine under thereaction conditions for preparing the polyamide are those where both theolefinic double bond and the amine group are made available under thereaction conditions, for example diamino monoamides or hydroxy aminoamides.

To prepare the polyamides of the invention, use may be made of theconventional process conditions for preparing polyamides from thecorresponding monomers, for example as described in DE-A-14 95 198,DE-A-25 58 480, EP-A-129 196, DE-A-19 709 390, DE-A-35 34 817, WO99/38908, WO 99/43734, WO 99/43732, WO 00/24808, WO 01/56984 or inPolymerization Processes, Interscience, New York, 1977, pp. 424-467, inparticular pp. 444-446.

In one preferred embodiment, the polymerization or polycondensation maybe carried out by the process of the invention in the presence of atleast one pigment. Preferred pigments are titanium dioxide, preferablyin the anatase or rutile crystalline form, or inorganic or organiccolorant compounds. The pigments are preferably added in amounts of from0 to 5 parts by weight, in particular from 0.02 to 2 parts by weight,based in each case on 100 parts by weight of polyamide. The pigments maybe introduced to the reactor with the starting materials or separatelytherefrom.

The polyamides of the invention may be linked in a controlled manner toobtain higher-molecular-weight polyamides. The formation ofhigh-molecular-weight linear polyamides is particularly advantageoushere. The formation of three-dimensionally crosslinked polyamides isalso particularly advantageous here.

The crosslinking may use processes known per se for the polymerizationof olefinically unsaturated compounds, for example addition of suitableinitiators or irradiation with UV light.

The polyamides of the invention, and their crosslinking products, may beused advantageously for producing fibers, films, or moldings whichcomprise this polyamide, or in particular consist of this polyamide.

EXAMPLES

In the examples, solution viscosity was measured as relative solutionviscosity in 96% sulfuric acid to DIN 51562-1 to -4.

For this, 1 g of polymer was weighed out for 100 ml of solution, 45 andthe throughflow time was measured in a Ubbelohde viscometer incomparison with the pure solvent.

Example 1

350 g (3.1 mol) of caprolactam, 35 g of demineralized water, and 0.8 g(7*10⁻³ mol) of 5-hexenoic acid (purity 99%) were heated under nitrogento an internal temperature of 270° C. in a laboratory autoclave, andthen immediately depressurized to atmospheric pressure within one hour,post-condensed for 60 minutes, and discharged.

The discharged polyamide was granulated, extracted with boiling water toremove caprolactam and oligomers, and then dried in a vacuum dryingcabinet. The dried extracted granules were heat-conditioned for varioustimes in the solid phase at 160° C. (5 h, 10 h, 20 h, 30 h).

Table 1 below shows the resultant relative solution viscosities aftervarious heat-conditioning times.

TABLE 1 Heat-conditioning time 0 h 10 h 15 h 20 h 30 h Relative solutionviscosity 2.42 2.70 2.79 2.84 2.98

Example 2

The melt behavior of three polyamide specimens from Example 1 wasstudied. For this, oscillatory shear measurements were made at 250° C.and melt viscosity measurements were carried out to ISO 11433. Thezero-shear viscosity η₀, i.e. the melt viscosity at zero shear, is afunction of the molar mass M_(n) for linear polyamides with Schulz-Florydistribution:η₀ −M _(n) ^(3,5)

The molar mass was determined by light scattering. FIG. 1 shows that thepolyamides prepared as in Example 1 are linear:

Example 3

Example 1 was repeated in a pressure vessel using the following mixture:400 kg (3571 mol) of caprolactam, 40 kg of demineralized water, and0.914 kg (8 mol) of 5-hexenoic acid. The polyamide discharged wasextracted, dried, and heat-conditioned in the solid phase to a relativesolution viscosity of RV=2.74.

An extruder was then used to compound 30% by weight of OCF 123 D 10 Pglass fibers (from OCF) and 7% by weight of Lupolen KR 1270 rubber (fromBASF Aktiengesellschaft) into the material (the percentages being basedon the finished compounded material). The relative solution viscosityafter compounding was 2.83.

Comparative Example

Example 3 was repeated with the modification that 0.592 kg (8 mol) ofpropionic acid was used instead of 5-hexenoic acid.

The relative solution viscosity after compounding was 2.83.

Melt volume rate (MVR) measurement to ISO 1133

Melt volume rate (MVR) measurements were carried out to ISO 1133 on thecompounded materials from Example 3 and from the comparative examples.The melt temperature here was 275° C. and the ram weight was 5 kg.

FIG. 2 shows the comparison of the melt volume rate for variousresidence times in the melt.

Flowability in two types of flow spirals (diameter 1.5 mm, 2 mm) wastested on the compounded materials from Example 3 and the comparativeexample. The temperature of the spirals was 280° C. Flow path wasmeasured in cm. Table 2 below shows the measurements:

TABLE 2 Example 4 Comparative example Flow spiral (1.5 mm) 25.9 cm 23.8cm Flow spiral (2 mm) 39.4 cm 36.8 cm

1. A polyamide which contains a monoolefinically unsaturatedmonocarboxylic acid of the formula CH₂═CH—(CH₂)₃—COOH chemically bondedat the end of the polymer chain via an amide group.
 2. A polyamide asclaimed in claim 1, where the content of the monoolefinicallyunsaturated monocarboxylic acid of the formula CH₂═CH—(CH₂)₃—COOH is inthe range from 0.001 to 2 mol %, based on 1 mole of amide groups of thepolyamide.
 3. A polyamide obtained by crosslinking a polyamide asclaimed in claim
 1. 4. A fiber, a film, or a molding, comprising apolyamide as claimed in claim
 1. 5. A process for preparing a polyamide,which comprises carrying out the reaction of monomers suitable forforming a polyamide to give a polyamide in the presence of amonoolefinically unsaturated monocarboxylic acid of the formulaCH₂═CH—(CH₂)₃—COOH.
 6. A process for preparing a polyamide, whichcomprises carrying out the reaction of oligomers suitable for forming apolyamide to give a polyamide in the presence of a monoolefinicallyunsaturated monocarboxylic acid of the formula CH₂═CH—(CH₂)₃—COOH.